Guides for running tape-like materials such as magnetic recording tapes, movie films, and microfilms are used as parts of audio or video cassette tape recorders, projectors, processing devices and as path rolls in production devices for such tape-like materials.
Guides for magnetic recording tapes, for example, which are incorporated in video cassettes and so forth, have heretofore been made of metallic materials, e.g., stainless steel, or plastic materials, e.g., polyacetal.
Recently, magnetic recording materials for use in magnetic recording tapes have been extensively researched and, nowadays, various magnetic recording materials, e.g., ferromagnetic iron-cobalt oxides, ferromagnetic chromium dioxide, ferromagnetic alloy powders, iron, cobalt, and nickel, and used. Magnetic recording tapes prepared by providing magnetic recording materials as described above on a plastic film base by techniques such as solution coating or vapor deposition have been developed and are now on the market. Furthermore, in order to improve the running properties of magnetic recording tapes, it has been attempted to provide a back coat containing fine inorganic particles with a plastic material as a binder.
In addition, a reduction in the thickness of plastic film bases for long-time recording has been made, and low-speed running of tapes has been employed. Under such circumstances, the requirements of guides for use in small-sized video cassettes and the like have been markedly changing.
Typical properties required for tape guides are as follows:
(1) They do not have magnetic properties;
(2) They have electrical conductivity and anti-static properties;
(3) Their coefficient of contact friction to magnetic recording tapes are low, so that the running speed of a tape can be maintained at a certain level;
(4) They cause low damage to tapes running thereon and cause only limited drop-out; and
(5) They have adequate mechanical properties to be incorporated into a cassette.
In general, ceramic materials are hard and of high abrasion resistance compared with metallic or plastic materials and, furthermore, ceramic materials have the advantage that they are free from corrosion on contact with air. Thus, attempts have been made to prepare guides for magnetic recording tapes using ceramic materials in place of conventional metallic materials. For example, Japanese Patent Publication No. 30766/76 discloses that an electrically conductive sintered molding of titanium monoxide has a coefficient of friction lower than metallic guides and it is not overly affected by temperature and humidity variations.
It has therefore been desired to develop superior ceramic materials meeting the above-described requirements for guides and, as a result of extensive research to prepare such ceramic materials, it has been found that, in addition to the type and the mechanical strength of the ceramic material used the finished surface of a guide made of a ceramic material has a significant influence on the above-described requirements.